Change Your Fork Oil

Posted July 28, 2016 by gdemo

Have you ever been riding your motorcycle down a beautiful country road, blasting through s-curves, but hit a bump and it feels like you went airborne?

I’ve been riding this ’78 Honda CB400 for about 4 years now. I’ve never been impressed with how it handles, but it’s a light bike. Lately though, it’s been a problem. I was hoping to wait until winter to do maintenance on the fork, but fork oil was leaking out of them and there was essentially no dampening effect at all.

So I hopped on to Bike Bandit and ordered all of the parts I’d need to replace the fork seals and fork oil. I ordered pretty much every little bolt, spring and gasket. It was like $100 in parts including fork oil.

Pulling the forks off was super easy. Obviously, the front wheel needs to come off and front fender and brake caliper.

I took this project as an opportunity to replace my brake line. I’m pretty sure I was running with the original 38-year-old brake line. A nice new braided line, should do the trick. And since I put on euro bars, I needed a little shorter line.

Once I pulled the front fork, it was just a matter of following the Clymer manual to dissemble them and replace all of the old parts. The fork oil that came out of those forks was disgusting. It was green and cloudy and stunk. I’m pretty sure water had gotten in there, it was bad.

One interesting thing was that during this project, I stumbled across this brilliant idea – how to install the fork oil seals without a fancy fork oil seal tool. When I read in the Clymer that I needed this special tool, I thought, “Someone has figured out a way to do this with without a tool.” I was right and it totally worked perfectly.

The effect of the new fork seals and oil was immediate. For instance, when I went to pull the front wheel off, I put a jack under the engine to lift the wheel off the ground and to support the bike while I’m performing my fork maintenance, it took like two pumps on the jack and the wheel was off the ground. But after putting in the seals and fork oil, I had to jack the bike up like 5 inches to get the wheel to line up with the fork so I could install the axle.

I haven’t even had it on the road yet, it’s raining now. I’ll give it a spin tomorrow morning. That new brake line seems tight. Now when I pull the brake level, it’s instant, and the lever doesn’t keep compressing as the old brake line expands under the pressure.

I often get people who say to me, “Aw man I want one of those old Hondas.” And I always say, “I love these old bikes, but unless you’ve got a fat bank account, or you really like working on motorcycles, you’re better off with a modern bike.”

Sure, I paid only $650 for the bike, but I’ve put in about $1,500 in parts and an equal amount in labor. Had I paid a mechanic to do all of the maintenance and repairs, I’d be $3,000 into this bike. It’s just not a $3,000 bike.

For me, half the fun of owning a bike is wrenching on it, so I love these old simple bikes. But if you don’t have a garage, interest or the skills to keep up on the maintenance, mechanics are expensive, and your bike will fall apart in a few years from neglect.

UPDATE: I did hit the road this morning with the bike, it is really nice to have that front fork working correctly. I feel like I’m more connected with the road now, rather than flying all over the place. It’s still a 1970s 400cc bike, but it rides much better now. And that new brake, also a major improvement.

UPDATE 2: After some riding, I felt like the brakes could be better, so I rebuilt the master cylinder. But still I didn’t like how that front brake was performing, so I purchased a new master cylinder from Dime City Cycles for $100 and the brakes work great now.